By now, you may have already seen some of the 'noisy GIFs' floating around the internet. They don't actually contain any sounds, but plenty of people seem to nonetheless be able to 'hear' the noise produced in the image.
New research is showing that the reason why so many people can seemingly 'hear' these sounds could be due to differences in the way the visual and audio processing parts of the brain work together in some people.
"Our latest study reveals normally-occurring individual differences in how our senses of vision and hearing interact," explains senior author and psychologist Elliot Freeman, from City University London.
"We found that people with 'visual ears' can use both senses together to see and also 'hear' silent motion, while for others hearing is inhibited when watching such visual sequences."
Does anyone in visual perception know why you can hear this gif? pic.twitter.com/mcT22Lzfkp— Lisa DeBruine 🏳️🌈 (@LisaDeBruine) December 2, 2017
GIFs don't have sound. They are silent video loops, but some people can 'hear' corresponding sounds - like the thump of an electricity pole or a splash of a wave.
We've written about the science of these noisy GIFs and other perceived sounds before, but this new research - by the same team - is looking deeper into what causes this sensation, called 'visual-evoked auditory response' (vEAR).
There are two popular hypotheses for why this might work. Either there are people who have extra connections between the visual and auditory processing areas of the brain, which causes vEAR; or everyone has the same connections, but only those with vEAR can use them.
The research team had just over 50 participants take part in a couple of experiments. They used a method called transcranial alternating current stimulation in two different wavelengths and measured people's 'hearing' responses to Morse code sequences.
For those that didn't experience vEAR, the stimulation currents did actually change the way their brains worked. If the stimulation was placed near the visual processing areas of the brain, the non-VEAR participants experienced reduced visual performance but improved audio performance.
This was vice-versa for when the stimulation was placed near the auditory processing parts of the brain.
Meanwhile, for those who did experience vEAR, there was no change.
Interestingly, the 50 participants included 16 musicians from the London Royal College of Music, and they were significantly more likely to report experiencing vEAR than non-musicians.
"We were also interested to find that, on average, participants with visual ear performed better on both visual and auditory tasks than those without. Perhaps their audio-visual cooperation benefits performance because more of the brain is engaged in processing visual stimuli," explains Freeman.
"Such cooperation might also benefit musical performance, explaining why so many of the musicians we tested reported experiencing visual ear."
This study was pretty small, so the researchers will have to investigate further with a bigger group of people, but even so, it's an interesting look into a super-weird phenomenon.